1. Field of the Invention
The present invention is concerned generally with a fluid-filled elastic mounting structure, and more particularly with a fluid-filled elastic mounting structure having a stopper device adapted to limit an amount of relative displacement between two support members of the structure when an excessive amount cf vibrational load is applied to the mounting structure.
2. Discussion of the Prior Art
There is known a mounting structure which is interposed between two members of a vibration transmission system, for flexibly connecting these two members or supporting one of the two members on the other member in a vibration damping and/or isolating fashion. As an example of such a mounting structure, laid-open Publication No. 57-9340 of unexamined Japanese Patent Application discloses a so-called fluid-filled elastic mounting structure including (a) a first and a second support member which are opposed to and spaced apart from each other in a load-receiving direction in which a vibrational load is applied to the mounting structure, (b) an elastic body interposed between the first and second support members, for elastically connecting the first and second support members, (c) a closure member which has a flexible portion and which is secured to the second support member, so as to cooperate with the elastic body to define therebetween a fluid chamber filled with a non-compressible fluid, (d) a partition assembly disposed within the fluid chamber, so as to divide the fluid chamber into a pressure-receiving chamber on the side of the elastic body, and an equilibrium chamber on the side of the closure member, and (e) an orifice for fluid communication between the pressure-receiving chamber and the equilibrium chamber. The orifice is tuned to a desired frequency range. The thus constructed fluid-filled elastic mounting structure is capable of damping or isolating the desired frequency range of vibrations, based on resonance of the fluid mass flowing through the orifice between the pressure-receiving and equilibrium chambers upon application of the vibrations.
The fluid-filled elastic mounting structure described above is used, for example, as an engine mount for attaching an engine or engine unit of a motor vehicle to the body of the vehicle. To facilitate the installation of such an engine mount on the vehicle, it has been proposed that the first support member includes a hollow cylindrical member which is positioned to extend in a direction perpendicular to the load-receiving direction of the mount. In this case, the first support member is attached to the engine unit such that a bolt or other connecting member fixed to the engine unit is inserted through the hollow cylindrical member of the first support member.
The mounting structure of the above type is generally required to include a stopper device adapted to limit an amount of deformation of the elastic body, or an amount of displacement of the two members connected to the first and second support members, upon application of an excessive amount of vibrational load to the mounting structure. To this end, the stopper device usually has a generally plate-like metallic member which extends from the second support member toward the first support member, so as to limit an amount of displacement of the first support member relative to the second support member in the load-receiving direction.
However, the applicant of the present invention has recognized the following problem encountered in respect of the stopper device as described above. Namely, since the fluid-filled elastic mounting structure having the pressure-receiving and equilibrium chambers is of relatively large size, the plate-like metallic stopper member used in the mounting structure tends to be accordingly large-sized in its length in particular, and have a relatively low degree of stiffness or rigidity and a relatively low resonance frequency. In consequence, upon application of a vibrational load to the mounting structure, there arise unfavorable noises and vibrations which are amplified due to resonance of the metallic stopper member. In this respect, it is extremely difficult to improve the rigidity of the stopper member by increasing its thickness, because of limitation in the installation space within the mounting structure.
In the fluid-filled elastic mounting structure having the hollow cylindrical member as the first support member as described above, the metallic stopper member is generally a large-sized, U-shaped strip, which extends from the second support member so as to surround the hollow cylindrical member such that the hollow cylindrical member is spaced apart from the stopper member by a suitable distance. In this case, the resonance frequency of the stopper member may be lowered to 600 Hz or lower, while the mounting structure practically used for the motor vehicle is required to isolate input vibrations having 600 Hz or lower frequencies. Thus, the resonance of the stopper member has great adverse influence upon the vibration isolating capability of the mounting structure.